Patent application title: Position Transmitter with Multi-Turn Position Acquisition

Abstract:

This invention relates to a position transmitter for the acquisition of
the position of a shaft, rotatable about an axis of rotation, comprising
an optical sensor arrangement with a plurality of sensor elements, in
which the plurality of sensor elements are provided for the acquisition
of the single-turn position of the shaft, and whereby part of the
plurality of sensor elements is provided for the acquisition, in
particular for the gearless acquisition, of the multi-turn position of
the shaft.

Claims:

1. Position transmitter for the acquisition of the position of a shaft
(4) which is rotatable about an axis of rotation (3), comprising an
optical sensor arrangement (12) with a plurality of sensor elements in
which the plurality of sensor elements are provided for the acquisition
of the single-turn position of the shaft, and wherein part of the
plurality of sensor elements is provided for the acquisition, in
particular for the gearless acquisition, of the multi-turn position of
the shaft.

2. Position transmitter according to claim 1, wherein all of the
plurality of sensor elements are provided for the acquisition of the
multi-turn position or wherein a further part of the plurality of sensor
elements is provided for the acquisition of at least one further
multi-turn position of the shaft and a comparison of the multi-turn
position and the at least one further multi-turn position occurs.

3. Position transmitter according to claim 1, which furthermore comprises
an illumination device (9), in particular a light-emitting diode
arrangement (9) with a light-emitting diode or with a plurality of
light-emitting diodes.

4. Position transmitter according to claim 1, which furthermore comprises
at least one, in particular exactly one, material measure (10) joined to
the shaft.

5. Position transmitter according to claim 4, wherein the at least one
material measure has an arrangement which interrupts the light path to
the part of the plurality of sensor elements corresponding to a part of a
whole revolution.

6. Position transmitter according to claim 1, which comprises a first
evaluation unit (14) for the evaluation of the single-turn position, a
second evaluation unit (15) for the evaluation of the multi-turn position
and a control/evaluation unit (16), in particular a microcontroller, for
the processing of the single-turn position and the multi-turn position.

7. Position transmitter according to claim 1, which has at least two
operating modes, wherein the at least two operating modes comprise a
normal mode on applying an external voltage supply and a power-saving
mode when the external voltage supply is switched off or fails.

8. Position transmitter according to claim 7, in which the position
transmitter is configured such that the first evaluation unit is switched
off in the power-saving mode.

9. Position transmitter according to claim 7, in which furthermore a
power source (17), in particular in the form of a non-rechargeable
battery or a rechargeable battery, and a device for monitoring the
external supply voltage and for changing over the power supply of the
position transmitter to the power source (17) when the external power
supply is switched off or fails, are provided.

10. Position transmitter according to claim 9 in combination with claim
3, which is configured such that in the power-saving mode the
illumination device can be supplied at least part of the time with
voltage, in particular, that in the case of a plurality of light-emitting
diodes in the power-saving mode at least part of the plurality of
light-emitting diodes can at least be supplied part of the time with
voltage.

11. Position transmitter according to claim 10, wherein the illumination
device, in particular the part of the plurality of light-emitting diodes,
can be supplied with voltage time-variably, in particular periodically or
pulsed with a variable frequency.

12. Position transmitter according to claim 10, which furthermore
comprises a movement measurement device, with which the speed and/or the
acceleration of the shaft can be measured so that, depending on the
measurement, the time-variable voltage supply of the illumination device,
in particular the frequency and/or frequency of occurrence and/or
duration of the voltage supply, can be realised.

13. Position transmitter according to claim 10 in combination with claim
6, wherein the control and evaluation unit is configured to realise the
time-variable voltage supply of the illumination device, in particular of
the part of the plurality of light-emitting diodes.

14. Position transmitter according to claim 1, wherein the optical sensor
arrangement is integrated on a sensor component, in particular an ASIC.

15. Position transmitter according to claim 14 in combination with claim
6, wherein the control and evaluation unit is also integrated in the
ASIC.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This patent application claims priority to European Patent
Application No. 09012831.5, filed Oct. 9, 2009, the entire disclosure of
which is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

[0002] This invention relates to a position transmitter for the
acquisition of the position of a shaft which is rotatable about an axis
of rotation.

STATE OF THE ART

[0003] Position transmission devices are used generally for the monitoring
and control of mechanical movement processes. For example, position
transmitters are used for the acquisition of rotational speed and the
control of motors. Position transmitters for the determination of angular
positions through the non-contacting single or multi-turn scanning of a
rotatable shaft are known in various embodiments.

[0004] The publication EP 0550794 describes a position transmitter for the
absolute-value position acquisition of a rotatable shaft, with a first
sensor arrangement and a first evaluation unit for the acquisition and
evaluation of the exact position of the shaft during a complete
revolution, i.e. the single-turn position, and with a second sensor
arrangement and a second evaluation unit for the acquisition and
evaluation of the number of complete shaft revolutions carried out, i.e.
the multi-turn position. In addition a third evaluation unit is provided
for forming an overall absolute value from the single-turn and from the
multi-turn position value and for the output of this overall absolute
value to a higher level system.

[0005] The acquisition of the single-turn position here occurs optically,
i.e. a material measure connected to the shaft influences, depending on
its position, the signals of an arrangement of photodiodes which are
illuminated by an LED. The acquisition of the multi-turn position here
occurs magnetically, i.e. a material measure connected to the shaft
influences, depending on its position, the signals of magnetic switching
elements. On switching off or with the failure of the external voltage
supply to the position transmitter, the acquisition of the single-turn
position is switched off. The supply to the multi-turn acquisition
continues to be maintained, provided by a battery in the position
transmitter. For the limitation of the power consumption the switching
elements are wired in series with a very high ohmic resistance, but are
continuously supplied with current. Switching the switching elements on
and off occurs depending on the position.

[0006] The publication EP 1462771 describes another position transmitter.
The acquisition of the single-turn position occurs magnetically via a
permanent magnet fixed centrally on the rotational axis and a
rotationally fixed magnetic sensor arrangement. The acquisition of the
multi-turn position also occurs magnetically. For the reduction of the
power consumption the evaluation unit only applies the current/voltage
periodically to the sensor parts for the time period of the measurement.
The evaluation is carried out by a microcontroller. This microcontroller
is operated during the pauses between the scannings in a power-saving
mode with reduced clock frequency and with the peripherals turned off.

[0007] Due to the magnetic principle of the multi-turn acquisition of
position transmitter devices known from the state of the art, substantial
disadvantages arise however when a position transmitter of this nature is
employed in the vicinity of a magnetic brake and the coupling of the
magnetic field in the switching elements leads to erroneous switching
pulses.

DESCRIPTION OF THE INVENTION

[0008] With respect to the state of the art, the object of this invention
is to realise a position transmitter which is insensitive to external
magnetic fields. In further developments of the invention the most
compact and economical construction and the longest possible service life
are to be achieved through an optimised design and optimised operation of
the sensor arrangements as well as through the acquisition and evaluation
electronics.

[0009] The above mentioned object is solved by a position transmitter
according to claim 1.

[0010] The claimed measurement device relates to a position transmitter
for the acquisition of the position of a shaft, rotatable about an axis
of rotation, comprising an optical sensor arrangement with a plurality of
sensor elements, in which the plurality of sensor elements are provided
for the acquisition of the single-turn position of the shaft, and whereby
part of the plurality of sensor elements is provided for the acquisition,
in particular for the gearless acquisition, of the multi-turn position of
the shaft.

[0011] The optical sensor arrangement with the plurality of sensor
elements here comprises preferably light-sensitive elements, such as for
example, photodiodes or phototransistors. The acquisition of the
multi-turn position thus also occurs optically. This facilitates complete
insensitivity of the position acquisition to magnetic fields. For the
acquisition of the single-turn position all of the plurality of sensor
elements are used, whereas only a part of the plurality of sensor
elements is used for the acquisition of the multi-turn position.

[0012] In a further development of the previously described position
transmitter also all the plurality of sensor elements can be provided for
the acquisition, in particular for the gearless acquisition of the
multi-turn position of the shaft. In this way the accuracy and
reliability of the measurement can be increased.

[0013] In another further development a further part of the plurality of
sensor elements is provided for the acquisition of at least one further
multi-turn position of the shaft, and a comparison of the multi-turn
position and the at least one further multi-turn position can occur. In
this way a data comparison with diagnostic possibilities can be made
available.

[0014] In a further development the position transmitter according to the
invention can furthermore comprise an illumination device, in particular
a light-emitting diode arrangement with at least one light-emitting
diode, that is with exactly one light-emitting diode or with a plurality
of light-emitting diodes. The light-emitting diode arrangement can, for
example, have exactly one light-emitting diode, the light of which is
acquired by all sensor elements. In another embodiment one light-emitting
diode or a plurality of light-emitting diodes can be provided for the
sensor elements in each case.

[0015] In another further development the position transmitter can
furthermore comprise at least one, in particular exactly one, material
measure joined to the shaft. The material measure, which is rotationally
fixed to the shaft, can include means for single-turn acquisition as well
as additionally means for multi-turn acquisition. In this way no separate
material measure is required for the multi-turn acquisition, which in
turn reduces the number of parts and increases the service life and
compactness of the position transmitter.

[0016] In another further development the at least one material measure
has an arrangement which interrupts the light path to the part of the
plurality of sensor elements corresponding to a part of a whole
revolution. In this way a multi-turn position can be acquired, for
example in quarter, half or whole revolutions.

[0017] Another further development is that the position transmitter
comprises a first evaluation unit for the evaluation of the single-turn
position, a second evaluation unit for the evaluation of the multi-turn
position and a control/evaluation unit for the processing of the
single-turn position and the multi-turn position. Thus preconditioning of
the signals from the optical sensor arrangement can take place in the
first or second evaluation unit and the calculation of an overall
absolute value can then take place in the control/evaluation unit.

[0018] In another further development the position transmitter can have at
least two operating modes, whereby the at least two operating modes
comprise a normal mode on applying an external power supply and a
power-saving mode when the external voltage supply is switched off or
fails. To reduce the power consumption, provision is made that the
operating mode of the multi-turn position acquisition is adapted on
switching off or failure of the external voltage supply, i.e. that for
example only pulse measurements are carried out (that is, short
measurements in comparison to the period of revolution). In addition
provision can be made that the single-turn position acquisition is
partially or completely switched off.

[0019] Advantageously, the position transmitter can be configured such
that the first evaluation unit is switched off in the power-saving mode.

[0020] In another further development the position transmitter can
furthermore comprise a power source, in particular in the form of a
non-rechargeable or rechargeable battery.

[0021] In this respect, firstly the sensor arrangement and/or the
illumination device can be supplied with voltage at least partially in
the power-saving mode. Since, for example, the photodiodes of the optical
sensor arrangement have however a negligible power consumption provision
is preferably made that it is continuously supplied with current/voltage.

[0022] Secondly, if a power source of this nature is provided, a device
for monitoring the external voltage supply and for switching over the
power supply of the position transmitter to the power source can be
provided when switching off or with the failure of the external power
supply.

[0023] In another further development the position transmitter can be
configured such that in the power-saving mode the illumination device can
be supplied at least part of the time with voltage, in particular, that
in the case of a plurality of light-emitting diodes in the power-saving
mode at least part of the plurality of light-emitting diodes can at least
be supplied part of the time with voltage.

[0024] For an efficient reduction of the power consumption it is
practicable to operate the actual actuator with high power consumption,
i.e. the operation of the illumination device (e.g. LED), in dependence
of the operating state with a variable switch-on time, such as for
example periodically or pulsed with a variable frequency. In contrast to
the state of the art, here periodic operation of the actuator, not the
sensor, occurs.

[0025] Another further development arises in that the illumination device,
in particular the part of the plurality of light-emitting diodes, can be
supplied with time-variable voltage, in particular periodically or pulsed
with a variable frequency.

[0026] In another further development the position transmitter can
furthermore comprise a movement measurement device, with which the speed
and/or the acceleration of the shaft can be measured so that, depending
on the measurement, the time-variable voltage supply of the illumination
device, in particular the frequency and/or frequency of occurrence and/or
duration of the voltage supply, can be realised. In addition a plurality
of operating modes or a plurality of operating frequencies can be
provided for controlling the LED. In this way a particularly advantageous
power-saving mode can be realised, because on switching off or with
failure of the external voltage supply, the shaft does not rotate or only
with a low speed and acceleration.

[0027] Another further development arises in that the control and
evaluation unit can be configured to carry out the time-variable voltage
supply of the illumination device.

[0028] In another further development the optical sensor arrangement can
be integrated on a sensor component, in particular an ASIC.

[0029] Another further development arises in that the control and
evaluation unit can be similarly integrated into the ASIC. In this way
the number of components in the position transmitter can be reduced and
the service life substantially increased. Simultaneously, the space
required by the sensors and electronics is reduced.

[0030] Further features and advantages of this invention are described in
the following with reference to the figures, which only illustrate
examples of embodiments and do not in any way represent the complete
extent of the invention. It is self-evident that the illustrated features
can be used within the scope of the invention in combinations other than
as described in the examples.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1 illustrates components of an example of a position
transmitter device according to the invention.

DESCRIPTION OF THE EMBODIMENTS

[0032] Optical scanning is used to acquire the single-turn position. The
acquisition of the multi-turn position also occurs optically. This is new
with respect to the state of the art described in the publications EP
0550794 and EP 1462771 and it facilitates complete insensitivity of the
position measurement with respect to magnetic fields.

[0033] Since now both the single-turn and the multi-turn position
acquisition are realised with optical sensor arrangements, there is also
the possibility that both sensor arrangements can be arranged integrated
on the same sensor module. Additionally, other devices, such as for
example evaluation units, interfaces, output drivers as well as units for
the operation, actuation and diagnosis of the LED, can also be integrated
on this sensor module. In this way the number of components of the
position transmitter can be extensively reduced and the service life or
the MTTF (Mean Time To Failure) can be substantially increased.
Simultaneously, the space required by the sensors and electronics is
reduced.

[0034] The material measure for the single-turn acquisition, which is
rotationally fixed to the shaft, can now also include means for the
multi-turn acquisition. In this way no separate material measure is
required for the multi-turn acquisition, which in turn reduces the number
of parts and increases the service life and compactness.

[0035] To reduce the power consumption provision is made that the
multi-turn position acquisition only carries out pulse measurements when
the external power supply is switched off or fails. Since the photodiodes
of the optical sensor arrangement, that is the sensors for the purpose of
EP 1462771, have however a negligible power consumption, provision is
preferably made that it is continuously supplied with current/voltage.
For an efficient reduction of the power consumption it is practicable to
operate the actual actuator with high power consumption, i.e. the
operation of the LED, in dependence of the operating state with a
variable switch-on time, such as for example periodically or pulsed with
a variable frequency. In contrast to EP 1462771, here periodic operation
of the actuator, not the sensor, occurs.

[0036] If complete evaluation in an application specific integrated
circuit (ASIC) is intended, the revolution acquisition can also be
limited to the time without an external voltage supply and it is also
taken over in the time with external voltage supply by the position
acquisition within one revolution.

[0037] The power source for the operation of the revolution counter on the
switch-off or the failure of the external voltage supply can, for
example, be an internal or external non-rechargeable battery or an
external or internal rechargeable battery.

[0038] In FIG. 1 a position transmitter device according to the invention
is illustrated according to an example of this invention.

[0039] The acquisition of the single-turn position within a revolution is
realised here with a sensor arrangement 12 with light-sensitive elements,
for example with photodiodes or phototransistors, which can be
illuminated through an optical material measure 10 by a light-emitting
diode arrangement 9. Part of the photodiodes or phototransistors is in
addition also used for the acquisition of the multi-turn position.

[0040] For example, in this embodiment a first evaluation unit 14 for the
evaluation of the single-turn position, a second evaluation unit 15 for
the evaluation of the multi-turn position (preconditioning of the
measurement signals) and a control and evaluation unit 16, e.g. for the
determination of an overall absolute value for the shaft position
(further processing of the signals from the first and second evaluation
units 14, 15), are provided.

[0041] The light-emitting diode arrangement 9 is actuated as required by
the control and evaluation unit 16, for example a microcontroller, via
constant current sources depending on the operating situation of the
position transmitter. Also the evaluation and further processing of the
single-turn position is actuated as required by the control and
evaluation unit 16 depending on the operating situation of the position
transmitter.

[0042] The evaluation and further processing of the single-turn position
is carried out as required by the control and evaluation unit 16
similarly according to the operating situation of the position
transmitter. With the application of the external voltage supply, i.e. in
normal operation, the single-turn position and also the multi-turn
position can be acquired.

[0043] The acquisition of the multi-turn position and/or the direction of
rotation, i.e. the acquisition of part of a revolution (for example
quarter, half, or complete revolutions), can be achieved via a special
embodiment of the material measure 10, which appropriately interrupts the
light path between the diodes and photo-receivers. In this connection the
material measure 10 can be used, which is also used for the acquisition
of the single-turn position.

[0044] With the application of the external voltage supply, i.e. in normal
operation, the light-emitting diode arrangement 9 can, for example, be
continuously energised. It can however also be operated with a variable
switch-on period, such as for example periodically or pulsed with a
variable frequency. It can in particular also be unenergised part of the
time.

[0045] When the external voltage supply is switched off or fails, i.e. in
the power-saving mode, the light-emitting diode arrangement 9 can be
operated with a variable switch-on time, such as for example periodically
or pulsed with a variable frequency, which is reduced compared to normal
operation. The frequency of occurrence and duration of energisation can
be increased with the first detected signal change.

[0046] A particularly advantageous embodiment is when the structures
necessary for the acquisition of the revolutions are also arranged on the
material measure 10, thus obviating any need for an additional material
measure or interrupting disc (refer to FIG. 2).

[0047] On switching off or with the failure of the external power supply
the revolution counting system is supplied by a power source. This power
source 17 can be a non-rechargeable or rechargeable battery. The power
source 17 can be integrated into the position transmitter or arranged
outside of the housing of the position transmitter.

[0048] The actuation of the LED, for example, frequency, frequency of
occurrence or duration of switch-on, can be dependent on the operating
parameters of the position transmitter, for example on the speed and/or
the acceleration of the shaft movement. To achieve this a device can be
present which facilitates the determination of the speed and/or the
acceleration also in the power-saving mode. In addition a plurality of
operating modes, for example a plurality of operating frequencies, can be
provided for controlling the LED. In this way a particularly advantageous
power-saving mode can be realised, because on switching off or with
failure of the external voltage supply, the shaft does not rotate or only
with a low speed and acceleration.

[0049] An additional, optimised expansion of the system can be realised by
integration of the photo-receivers in an opto-ASIC. Through the higher,
achievable processing speed in the opto-ASIC the power consumption in the
battery mode can be further reduced and the admissible limiting frequency
of the scanning system increased.